| Traditionally,in order to avoid the interference effect of wireless transmitting node on the receiver link in the frequency domain or time domain,frequency division or time division duplex mode is mainly used.More recently,the proposed full-duplex technology is mainly based on the interference cancellation method,which can save the cost of frequency or time slot resources in frequency division or time division duplex,so the spectrum efficiency can be significantly improved.However,the biggest problem faced by full-duplex wireless communication is that when the transmitter operates with higher power signal,it will cause strong interference to the weak desired signal of the local receiver,which is usually referred to as "self-interference".As the transmission power increases,due to the inherent nonlinear distortion and memory effect of transmitter chain analog components and integrated modules,such as mixer and power amplifier of broadband full-duplex system,the self-interference of wireless full-duplex receiver will be difficultly suppressed.In particular,the next generation cellular mobile communication systems will enter the field of millimeter wave and terahertz frequency bands,with higher frequency bands and wider bandwidths.With the further increase of transmission power,the influence of nonlinear effects will become more and more obvious,which will seriously decrease the performance of nonlinear interference cancellation.Therefore,it is very urgent to study the large bandwidth nonlinearity correction methods for full-duplex communication.In addition,with the increase of the working frequency band of the full-duplex systems,the time-frequency synchronization error will also significantly affect the interference cancellation capability of the receiver chain,resulting in a reduction in the actual interference cancellation performance of the systems.The specific contributions are as follows:（1）The performance of the two main digital nonlinear interference cancellation methods for full-duplex system is studied.Firstly,the two main realization methods of RF signal feedback and digital nonlinear modeling are analyzed,including system model and its signal analysis of nonlinear interference cancellation.Secondly,it mainly analyzes signal models of two digital nonlinear interference cancellation methods,and deduces the theoretical expression on interference cancellation performance.Finally,the pros and cons of the two nonlinear interference cancellation methods are analyzed,and some numerical simulation results of large-bandwidth nonlinear full-duplex systems under different simulation parameters are given.（2）The nonlinear correction method for full-duplex broadband receiver and transmitter is studied.Aiming at the broadband nonlinear effect characteristics of power amplifiers in the transmission,a digital nonlinear correction method at the receiver link is proposed to reduce the nonlinear distortion of the transmitter.This method first trains a nonlinear correction module using some known transmitted symbols and then inserts the trained correction module into the receiver link to compensate for the nonlinear distortion by the analog components at the transmission link,so as to improve the signal quality at the receiver side.The proposed method is performed at the symbol level without any oversampling,and does not require additional feedback loops.As transmission power increases,the modulation schemes with higher spectrum efficiency,can still be adopted,and when applied to millimeter wave and terahertz frequency bands,the transmission distance can be significantly increased.Furthermore,in full-duplex broadband communication,if the traditional digital predistortion technology is used to perform nonlinear correction on the nonlinear interference signal caused by the power amplifier of the transmission link,the sampling rate of the digital-to-analog converter and the analog-to-digital converter is usually required to reach the 5 times of signal bandwidth,thus the fifth-order nonlinear distortion can be effectively characterized,which is unacceptable for millimeter-wave and terahertz frequency bands.Therefore,aiming at the linearization of the transmitter,a low-rate method and the corresponding digital predistortion algorithm of the analog-to-digital converter are proposed to realize the nonlinear distortion correction at the transmitter link.（3）The design of low sampling rate system for broadband nonlinear full-duplex communication is studied.Aiming at the problem of high sampling rate of the transmission link of the full-duplex broadband nonlinear communication system,a low sampling rate digital predistortion technology implementation scheme is proposed,which can not only reduce the limitation on the analog bandwidth,but also reduce the sample rate requirements of the transmission link digital-to-analog converter.Compared with the existing bandwidth-limited digital predistortion methods,which only reduce the sampling rate of the transmitter by suppressing part of the bandwidth nonlinear distortion,the proposed system scheme can utilize three frequency segments with low hardware cost and a relatively low sampling rate.The three frquency branches is used to transmit in-band,lower sideband and upper sideband predistortion signals respectively,with full bandwidth linearization performance.（4）The synchronization error processing technology of full-duplex broadband communication system is studied.Firstly,the influence of the time-frequency synchronization error on the interference cancellation performance of the full-duplex system is discussed.Based on the Gaussian channel model,the influence of the time-frequency synchronization error of the cooperative jamming signal on the communication performance of the receiver link is theoretically analyzed.The simulation verification is carried out to provide theoretical support for the design of practical full-duplex communication system.Furthermore,self-interference cancellation methods in full-duplex analog domain and digital domain under the constraint of time delay are proposed,and the corresponding signal analysis model,parameter optimization criterion,channel estimation algorithm,etc.are given.This dissertation studies the nonlinear correction and synchronization error processing technology of full-duplex broadband transmission and reception.From the perspective of engineering practice,it involves the constraint analysis of actual non-ideal factors,the design of some methods and algorithms,etc.The obtained methods and results can give some helpful references to full-duplex high-frequency broadband communication,which can be applied to the new generation cellular systems operating in the millimeter-wave and terahertz frequency bands. |
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